Synthesis and characterization of β,β′-linked porphyrin-chlorin heterodimers and their metallic complexes

Two β,β′-linked porphyrin-chlorin heterodimers have been successfully synthesized with 4-fluorophenyl or 4-chlorophenyl substituted aldehyde as starting reagents. But those aldehydes with bulkier substituents did not lead to the corresponding heterodimers. These porphyrin-chlorin heterodimers and their metallic complexes have been characterized by X-ray crystallography. In all the structures, the pyrroline group in chlorin moiety and the pyrrole group in porphyrin moiety are directly connected by a single bond. Pyrroline ring has two sp[Formula: see text] hybridized carbons. The direct bonding makes the porphyrin and chlorin moieties closely contact with each other, pyrroline group and the pyrrole group forms a dihedral angle of ~70°. If porphyrin-chlorin heterodimers have bulkier substituents, the close contact could cause too much repulsion. That is probably why they can not be synthesized. For nickel complexes, the chlorin planes show large saddling and moderate ruffling conformation. The C–H⋯[Formula: see text] interaction could contribute to the saddling conformation. The distorted core makes dihedral angles and metal to metal distances between porphyrin and chlorin plane much smaller than those in their copper complexes. Their NMR, UV-visible and fluorescence spectral data have also been briefly discussed.